<template>
  <view class="u-count-num" :style="{
			fontSize: fontSize + 'rpx',
			fontWeight: bold ? 'bold' : 'normal'
		}">{{ displayValue }}</view>
</template>

<script>
/**
 * countTo 数字滚动
 * @description 该组件一般用于需要滚动数字到某一个值的场景，目标要求是一个递增的值。
 * @tutorial https://www.uviewui.com/components/countTo.html
 * @property {String Number} start-val 开始值
 * @property {String Number} end-val 结束值
 * @property {String Number} duration 滚动过程所需的时间，单位ms（默认2000）
 * @property {Boolean} autoplay 是否自动开始滚动（默认true）
 * @property {String Number} decimals 要显示的小数位数，见官网说明（默认0）
 * @property {Boolean} use-easing 滚动结束时，是否缓动结尾，见官网说明（默认true）
 * @property {String} separator 千位分隔符，见官网说明
 * @property {String} color 字体颜色（默认#303133）
 * @property {String Number} font-size 字体大小，单位rpx（默认50）
 * @property {Boolean} bold 字体是否加粗（默认false）
 * @event {Function} end 数值滚动到目标值时触发
 * @example <u-count-to ref="uCountTo" :end-val="endVal" :autoplay="autoplay"></u-count-to>
 */
export default {
  name: 'u-count-to',
  props: {
    // 开始的数值，默认从0增长到某一个数
    startVal: {
      type: [Number, String],
      default: 0
    },
    // 要滚动的目标数值，必须
    endVal: {
      type: [Number, String],
      default: 0,
      required: true
    },
    // 滚动到目标数值的动画持续时间，单位为毫秒（ms）
    duration: {
      type: [Number, String],
      default: 2000
    },
    // 设置数值后是否自动开始滚动
    autoplay: {
      type: Boolean,
      default: true
    },
    // 要显示的小数位数
    decimals: {
      type: [Number, String],
      default: 0
    },
    // 是否在即将到达目标数值的时候，使用缓慢滚动的效果
    useEasing: {
      type: Boolean,
      default: true
    },
    // 十进制分割
    decimal: {
      type: [Number, String],
      default: '.'
    },
    // 字体颜色
    color: {
      type: String,
      default: '#303133'
    },
    // 字体大小
    fontSize: {
      type: [Number, String],
      default: 50
    },
    // 是否加粗字体
    bold: {
      type: Boolean,
      default: false
    },
    // 千位分隔符，类似金额的分割(￥23,321.05中的",")
    separator: {
      type: String,
      default: ''
    }
  },
  data() {
    return {
      localStartVal: this.startVal,
      displayValue: this.formatNumber(this.startVal),
      printVal: null,
      paused: false, // 是否暂停
      localDuration: Number(this.duration),
      startTime: null, // 开始的时间
      timestamp: null, // 时间戳
      remaining: null, // 停留的时间
      rAF: null,
      lastTime: 0 // 上一次的时间
    };
  },
  computed: {
    countDown() {
      return this.startVal > this.endVal;
    }
  },
  watch: {
    startVal() {
      this.autoplay && this.start();
    },
    endVal() {
      this.autoplay && this.start();
    }
  },
  mounted() {
    this.autoplay && this.start();
  },
  methods: {
    easingFn(t, b, c, d) {
      return (c * (-Math.pow(2, (-10 * t) / d) + 1) * 1024) / 1023 + b;
    },
    requestAnimationFrame(callback) {
      const currTime = new Date().getTime();
      // 为了使setTimteout的尽可能的接近每秒60帧的效果
      const timeToCall = Math.max(0, 16 - (currTime - this.lastTime));
      const id = setTimeout(() => {
        callback(currTime + timeToCall);
      }, timeToCall);
      this.lastTime = currTime + timeToCall;
      return id;
    },

    cancelAnimationFrame(id) {
      clearTimeout(id);
    },
    // 开始滚动数字
    start() {
      this.localStartVal = this.startVal;
      this.startTime = null;
      this.localDuration = this.duration;
      this.paused = false;
      this.rAF = this.requestAnimationFrame(this.count);
    },
    // 暂定状态，重新再开始滚动；或者滚动状态下，暂停
    reStart() {
      if (this.paused) {
        this.resume();
        this.paused = false;
      } else {
        this.stop();
        this.paused = true;
      }
    },
    // 暂停
    stop() {
      this.cancelAnimationFrame(this.rAF);
    },
    // 重新开始(暂停的情况下)
    resume() {
      this.startTime = null;
      this.localDuration = this.remaining;
      this.localStartVal = this.printVal;
      this.requestAnimationFrame(this.count);
    },
    // 重置
    reset() {
      this.startTime = null;
      this.cancelAnimationFrame(this.rAF);
      this.displayValue = this.formatNumber(this.startVal);
    },
    count(timestamp) {
      if (!this.startTime) this.startTime = timestamp;
      this.timestamp = timestamp;
      const progress = timestamp - this.startTime;
      this.remaining = this.localDuration - progress;
      if (this.useEasing) {
        if (this.countDown) {
          this.printVal = this.localStartVal - this.easingFn(progress, 0, this.localStartVal - this.endVal, this.localDuration);
        } else {
          this.printVal = this.easingFn(progress, this.localStartVal, this.endVal - this.localStartVal, this.localDuration);
        }
      } else {
        if (this.countDown) {
          this.printVal = this.localStartVal - (this.localStartVal - this.endVal) * (progress / this.localDuration);
        } else {
          this.printVal = this.localStartVal + (this.endVal - this.localStartVal) * (progress / this.localDuration);
        }
      }
      if (this.countDown) {
        this.printVal = this.printVal < this.endVal ? this.endVal : this.printVal;
      } else {
        this.printVal = this.printVal > this.endVal ? this.endVal : this.printVal;
      }
      this.displayValue = this.formatNumber(this.printVal);
      if (progress < this.localDuration) {
        this.rAF = this.requestAnimationFrame(this.count);
      } else {
        this.$emit('end');
      }
    },
    // 判断是否数字
    isNumber(val) {
      return !isNaN(parseFloat(val));
    },
    formatNumber(num) {
      // 将num转为Number类型，因为其值可能为字符串数值，调用toFixed会报错
      num = Number(num);
      num = num.toFixed(Number(this.decimals));
      num += '';
      const x = num.split('.');
      let x1 = x[0];
      const x2 = x.length > 1 ? this.decimal + x[1] : '';
      const rgx = /(\d+)(\d{3})/;
      if (this.separator && !this.isNumber(this.separator)) {
        while (rgx.test(x1)) {
          x1 = x1.replace(rgx, '$1' + this.separator + '$2');
        }
      }
      return x1 + x2;
    },
    destroyed() {
      this.cancelAnimationFrame(this.rAF);
    }
  }
};
</script>

<style lang="scss" scoped>
@import "../../libs/css/style.components.scss";

.u-count-num {
  display: inline-block;
  text-align: center;
}
</style>
